Batteries, including lithium-ion batteries, may be used for a variety of target applications that require relatively higher levels of energy storage, power delivery and recharge cycle capability. These applications may include, for example, hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), solar/wind (renewable) power smoothing, power grid frequency regulation, power grid storage for peak shaving and other applications. Parties, ranging from manufacturers to distributors to end users of these batteries, have an interest in determining the useful life span of the batteries and the charge capacity degradation that has occurred in an aged battery (e.g., the state of health or SOH of the battery). Accurate SOH determination may facilitate dual-use of battery systems and improve the value estimation of the battery after retirement from a primary application. Unfortunately, the lifespan may vary considerably depending on the target application and in particular the drive cycle (rate of charge/discharge) of the application, which may include, for example, the depth of discharge and the charge and discharge rates.
Existing battery test procedures generally involve some combination of voltage, current, resistance, impedance and temperature measurements. These procedures typically do not provide the desired level of accuracy across a broad range of battery chemistries.
What is needed, therefore, are methods and systems for estimation of the state of health or capacity degradation of an aged battery that provide improved accuracy, reliability and efficiency.